The present invention relates to a window glass antenna for vehicles which is mounted on a window glass of a vehicle such as an automobile.
A conventional vehicle window glass antenna is assembled by attaching an antenna element having a given pattern and constituted of narrow thin-film conductors on a rear window of an automobile.
Usually a defogger is attached to the rear window in order to defog a glass of the window. The defogger includes a plurality of horizontal wires constituted of narrow thin-film conductors which are arranged in parallel and at almost regular intervals on the rear window. First ends of the horizontal wires are connected together by one of paired bus bars, while second ends thereof are connected together by the other bus bar.
If a direct-current power supply voltage is applied to the bus bars from a car-mounted battery (12V), the horizontal wires generate heat to prevent the fogging of the window glass due to condensation.
The vehicle window glass antenna is provided between the uppermost portion of the defogger and the window frame. The narrow thin-film conductors are formed on the window glass in a given pattern such that the antenna can receive radio waves of a predetermined frequency, and used as antenna elements. A feeding point of the antenna elements is connected to a tuner of a receiver set through a feeder formed of a coaxial cable.
In most cases, a desired antenna characteristic cannot be obtained from the above conventional vehicle window glass antenna, since the surroundings of the antenna are varied with vehicle types and other conditions, even though the antenna itself is accurately assembled based on a fixed standard. The window glass is usually surrounded with a metallic car body; therefore, it is difficult to design the antenna only by the antenna theory. For this reason, the actual state is that the antenna characteristic such as an impedance is adjusted using a cut-and-try method. More specifically, when the antenna is mounted on the window glass, a characteristic measuring instrument, such as an impedance meter, is connected to an end portion of the feeder in place of the tuner, and the antenna characteristic is controlled by correcting the pattern, length or the like of the antenna using the cut-and-try method.
A technique of utilizing the defogger as an antenna element is also proposed. In this technique, too, the antenna characteristic has to be adjusted using the cut-and-try method in order to acquire a desired antenna characteristic.
As described above, in the conventional vehicle window glass antenna, the antenna characteristic had to be adjusted using the cut-and-try method according to the types of vehicles on which the antenna was to be mounted, in order to obtain a desired antenna characteristic. Furthermore, the conventional antenna had the problem that it was very difficult and took a long period of time to adjust a frequency band of use by the above cut-and-try method.